The purpose of the proposed research is to develop a pain assessment technique for use in primates based on signal detection theory. Signal detection theory provides; a) an estimate of the sensitivity of the nervous system (called sensory sensitivity or d') for detecting or discriminating between stimuli and b) a measure (called response bias or beta) of the influence of factors such as expectation, motivation or attention which can influence the response to sensory stimuli. These two parameters are assumed to be independent. The latency and force with which monkeys respond to noxious electrocutaneous pulses will be used as ratings of pain intensity. Relative operating characteristic (ROC) functions will be derived from these ratings in order to obtain independent estimates of pain sensitivity and response bias. Values of pain sensitivity will then be determined as a function of stimulus intensity and skin location of stimulus application. In addition, the role of A delta and C fibers will be differentiated in regard to their relative contributions to sensitivity and response bias. Measures of pain sensitivity and response bias will then be obtained under the influence of experimental manipulations known to affect pain behavior. These manipulations will include the administration of analgesic and nonanalgesic drugs, administration of placebo, brain stimulation, frontal lobe ablation and acupuncture. By investigating a large number of subjects under a variety of experimental conditions and over a wide range of painful stimulus intensities we expect to firmly establish the validity and general applicability of this approach for the study of pain perception.